U.S. Pat. No. 5,014,926 discloses a seat belt retractor having a rotatable spool upon which seat belt webbing is wound. The webbing has a retracted position in which it is located beside a vehicle seat, and has an extended position in which it extends around an occupant of the seat. The spool in the retractor rotates in an unwinding direction as the webbing is withdrawn from the retractor upon movement of the webbing from the retracted position toward the extended position. A rewind spring in the retractor rotates the spool oppositely in a winding direction to retract the webbing back into the retractor, and thus to move the webbing back from the extended position toward the retracted position.
The retractor disclosed in the '926 patent includes a locking mechanism which operates to block rotation of the spool in the unwinding direction upon the occurrence of a vehicle collision. The locking mechanism includes a lock bar which is movable into a locking position in which it blocks rotation of the spool in the unwinding direction. The locking mechanism further includes a lock bar actuator which moves the lock bar into the locking position. The actuator is supported for limited rotation in the retractor. A cam portion of the actuator moves the lock bar into the locking position upon rotation of the actuator.
When the vehicle experiences a collision, a vehicle occupant moves suddenly against the seat belt webbing that is extended around the occupant. This causes the spool to accelerate in the unwinding direction. A web sensitive mechanism in the retractor responds to such acceleration of the spool by coupling the actuator rotationally with the spool. The actuator then rotates a short distance with the spool, and the cam portion of the actuator moves the lock bar into the locking position. The retractor thus operates to block rotation of the spool in the unwinding direction in response to sudden movement of the webbing which indicates the occurrence of a collision.
Additionally, when the vehicle experiences a predetermined amount of deceleration which indicates the occurrence of a collision, a vehicle sensitive mechanism in the retractor responds to such deceleration by coupling the actuator with the spool. The actuator then rotates a short distance with the spool, and the cam portion of the actuator moves the lock bar into the locking position. The retractor thus operates further to block rotation of the spool in the unwinding direction in response to vehicle deceleration indicative of a collision.